Electronic devices such as pagers and cellular telephones sometimes have a two-part foldable housing that includes a body portion and a flip portion. The body portion houses most of the electronics, and the flip portion folds over the body portion. The flip portion typically contains a display and an antenna.
A hinge control mechanism is typically used to mechanically couple the body portion to the flip portion. The hinge control mechanism allows the flip portion to be rotated from a closed position (in which the flip portion covers the body portion) to an open position. The typical hinge control mechanism includes a shaft that rotates relative to a spring which the shaft bears on. When the flip portion is opened somewhat, the force generated by the spring being deflected by the shaft urges the flip portion to a fully open position and holds it in that position.
Electronic devices such as pagers and cellular telephones typically have a preset, opened position for active operation; and they lack provision for remaining opened in any position other than the preset position.
Electronic devices such as foldable portable computers typically lack a preset, opened position; instead, they have a frictional mechanism that allows the flip portion to be set at a plurality of positions with respect to the body portion.